Chlorofluorocarbon (CFC) heat exchanging compositions, referred to hereinafter as refrigerants, currently used in heat pumps, air conditioners, and refrigerators, are now known to have serious environmental effects due to destructive reactions with ozone in the Earth's atmosphere. It is believed that the chlorine atom in these refrigerants is the "culprit" which leads to the destruction of the ozone layer. Thus, refrigerant containing any chlorine atom as part of its chemical composition will likely be prohibited for use in air conditioners. NonCFC refrigerants which have no Cl atom in their chemical structure, such as fluorocarbons, will likely be used to replace CFC refrigerants currently in use.
It is necessary to locate and repair minute leaks of refrigerants in heat exchanging equipment. Currently available refrigerant leak detectors are generally based on the detection of the chlorine constituent of the molecule. For example, a common CFC leak detector utilizes a small flame impinging upon a copper plate. When CFC is present, the flame will be green in color, due to the chlorine constituent in the CFC.
Other commonly-used detection methods include heated anode and corona suppression. Heated anode leak detectors employ a red-hot platinum and ceramic heater element which releases positive ions. These positive ions are collected on a negatively charged cylindrical cathode to provide a standing current. The presence of CFC in sampled gas increases the emission of positive ions which then triggers the leak signal. The corona suppression leak detector applies a voltage across a sensor element to produce a corona (spark) which generates a standing current. The presence of CFC in sampled gas inhibits the corona spark which triggers a leak signal. Because the use of red-hot elements or sparks raises the possibility of undesired ignition, these types of detectors are not suitable for use in areas where flammable or explosive gas is likely to be present. These detectors are not suitable for detecting chlorine free refrigerants. Also, no intrinsic leak signal amplification appears to be involved in those leak detectors.
A reliable, sensitive, and simple instrument which can be used to detect chlorine-free refrigerant leaks of less than one ounce per year from heat exchange equipment will soon be essential to the heat exchange industry.
Furthermore, awareness of the sensitivity of the environment to the presence of small amounts of hazardous, toxic, or otherwise undesirable materials has created a need for new methods and apparatus for detecting small quantities of these materials in suspect localities. Certain of these materials are comprised of electronegative species, which can form a basis for their detection in very low concentrations. Examples of these materials are polychlorinated biphenyls (PCB's), carbon tetrachloride, and trichloroethylene (TCE). A reliable, sensitive, and simple instrument which can be used to detect one part per million or less of these materials in the atmosphere is essential to the protection of the environment.